Inflatable airbag

ABSTRACT

An inflatable side curtain airbag for a passenger vehicle is provided. The airbag incorporates a new diode design that restricts gas flow, creating a plurality of substantially isolated cells. A delivery tube delivers gas to the cells through a plurality of outlet orifices that open to the cells. Upon inflation of the cells with a gas, flow of gas between each of the plurality of substantially isolated cells is restricted during occupant loading.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to previously-filed provisionalapplication Ser. No. 60/591,301 filed Jul. 26, 2004, which is relied onand incorporated herein fully by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to side curtain airbags used forside impact and rollover protection, although the designs also may beuseful in other airbag application types.

Side curtain airbags generally deploy downward from a stowed positionwithin the roofline of vehicle and inflate between the occupant and thevehicle interior side structure, such as the side windows and the A, Band/or C pillars.

A side curtain airbag generally consists of two fabric panels eithersewn or interwoven together to create inflatable cells. These cells areinflated during an accident to provide the desired side restraint. Aside curtain may have a plurality of cells in various arrangements.Typically, inflatable cells in the range of two inches to as much aseight inches in inflated thickness may be created by sewn or interwovenseams connecting the fabric layers. The cell's inflated thickness (orcurtain thickness) is the distance between the two fabric panels wheninflated.

Conventional airbag curtain designs have “open flow” between chambercells. Open flow is characterized by the gas within a cell havingsubstantially open fluid communication with adjacent cells. Thisconfiguration allows the gas to uniformly fill the entire airbag becausethe gas distributes among all of or most all of the airbag cells orinflated regions. An example of an open flow conventional airbag isdisclosed in FIG. 2 of U.S. Pat. No. 6,481,743 to Tobe et al., theentire disclosure of which is herein fully incorporated by reference.

SUMMARY

The present invention recognizes and addresses considerations of priorart constructions and methods and provides a novel inflatable airbag fora passenger vehicle.

The present invention provides an airbag comprising a plurality ofsubstantially isolated cells and a delivery tube having a plurality ofoutlet orifices. The orifices open to the cells, thereby allowing gasfrom a gas source to enter the cells. In some embodiments, the gas isstored in an inflator that is activated by a sensor in the event of anaccident.

At least one outlet orifice of the delivery tube is configured to supplya gas to each of the plurality of substantially isolated cells. Uponinflation of the cells, flow of gas between cells during occupantloading is restricted.

In some embodiments, the delivery tube may incorporate scoops to aid inthe inflation of the cells. Such scoops are designed to channel gas intothe cells while restricting backflow from the cells into the deliverytube. In addition, sewn seam optimization of the present invention maybe used to reduce the amount of gas communication between adjacent cellsand between the cells and the atmosphere.

The accompanying drawings, incorporated in and constituting part of thisspecification, illustrate one or more embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference the appended drawings,in which:

FIG. 1 is a side view of a vehicle with an inflated side curtain airbag;

FIG. 2 is an elevational view of the airbag in FIG. 1;

FIG. 3 is a cut-away view taken along line 3-3 of FIG. 2;

FIG. 4 is a cut-away view taken along line 4-4 of FIG. 2;

FIG. 5 is an elevational view of another embodiment of a side curtainairbag in accordance with the present invention; and

FIG. 6 is a cut-away view taken along line 6-6 of FIG. 5.

Repeat use of reference characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to presently preferred embodimentsof the invention, one or more examples of which are illustrated in theaccompanying drawings. Each example is provided by way of explanation ofthe invention, not limitation of the invention. In fact, it will beapparent to those skilled in the art that modifications and variationscan be made in the present invention without departing from the scopeand spirit thereof. For instance, features illustrated or described aspart of one embodiment may be used on another embodiment to yield astill further embodiment. Thus, it is intended that the presentinvention covers such modifications and variations as come within thescope of the appended claims and their equivalents.

Referring to the drawings, and particularly to FIG. 1, a typical vehicle10 is shown. Vehicle 10 includes an A-pillar 12, a B-pillar 14, and aC-pillar 16. A side curtain airbag 18 in accordance with the presentinvention extends between A-pillar 12 and C-pillar 16. In FIG. 1, airbag18 is shown in an inflated state. In this regard, an inflator 20provides a gas necessary to inflate airbag 18. Inflators 21 and 23 areshown in FIG. 1 to display alternative locations for the inflator. Thus,the inflator may be located in the B-pillar, in the C-pillar, in theroof, or in another suitable location within vehicle 10.

Before airbag 18 is deployed, it may be stored within roof rail 22 ofvehicle 10. Optionally, tethers 24 and 26 may be used to restrain airbag18. In the embodiment shown in FIG. 1, tethers 24 and 26 attach at oneend to airbag 18 and at the other end to the body of the vehicle.

Referring now to FIG. 2, further details of side curtain airbag 18 canbe most easily explained. Airbag 18 includes a plurality ofsubstantially isolated cells 28, 30, 32, 34, 36, 38, and 40. Cells 28,30, and 32 make up a rear bank of cells between B-pillar 14 and C-pillar16, while cells 34, 26, 38, and 40 make up a front bank of cells betweenA-pillar 12 and B-pillar 14. Area 42 is not inflated because an occupantis less likely to come into contact with that area. In some embodiments,however, area 42 may be a cell, or may inflate at a time later than theother cells.

Continuing to refer to FIG. 2, tabs 44 are provided in this embodimentto attach airbag 18 to roof rail 22. Instead of tabs 44, any suitablemethod of attachment may be used. A delivery tube 46 having a pluralityof outlet orifices 48 is also provided. In the illustrated embodiment,outlet orifices 48 are formed as scoops. Orifices 48 open to cells 28,30, 32, 34, 36, 38, and 40. To reduce turbulence within tube 46 and tobetter distribute the gas, outlet orifices 48 may be staggered abouttube 48. Such staggering can be seen in FIG. 4. Delivery tube 46 issealed at 50. Gas from inflator 20 enters delivery tube 46 at end 52 andis distributed into the cells through outlet orifices 48.

Referring now to FIGS. 2, 3, and 4, the mating of delivery tube 46 withairbag 18 can be described. In this embodiment, tube 46 is inserted intothe top portion of airbag 18. A top perimeter seam 54 runs along the topof airbag 18 and forms an upper restraint for tube 46. A series of sewnovals 56 are formed by stitching 57 (FIG. 3) between the cells. The topsof ovals 56 form a substantially tight fit with the bottom of tube 46.In this context, “tight” does not mean that no gas is able to flowbetween ovals 56 and tube 46. Instead, “tight” refers to a close-fitthat may be optimized to allow some gas flow between adjacent cells.Along with continuous seam 58 and seams 66, 68, 70, 72, and 74, ovals 56form cells 28, 30, 32, 34, 36, 38, and 40. Any of the sewn seams may besingle stitched, double stitched, or attached in another appropriatemanner, depending on the strength and air-tightness requirements of theairbag. Airbag 18 has a thickness t (FIGS. 3 and 4), which may vary overthe cells.

Referring specifically to FIG. 4, outlet orifice 48, formed as a scoop,can be seen. The orientation of orifice 48 in FIG. 4 is somewhatstaggered in that it is rotated at various angular positions around thetube periphery. The scoops preferably are rotated at various angularpositions about tube 46 to better or more effectively capture andchannel the gas flowing within the tube into the cell.

FIG. 5 shows a second embodiment of the present invention. In thisembodiment, airbag 76 is inflated by inflator 78, which is positioned inthe B-pillar adjacent the center of deployed airbag 78. Inflator 78connects with delivery tube 80 at an intermediate location along itslength, in this case near the longitudinal center. In thisconfiguration, both of ends 82 and 84 are sealed, forcing gas into eachof cells 86, 88, 90, 92, and 94 upon inflation. Tethers 96 and 97connect airbag 76 to the vehicle body. Depending on the vehicle orapplication, other configurations of the present invention may includeembodiments with more than two banks of cells.

Continuing to refer to FIG. 5, it can be seen that a circle 98 is sewninto cell 88. A seam 100 connects circle 98 to seam 102, which formspart of the cell's perimeter. Seam 100 partially separates cell 88 andmay be designed to reduce the volume and thickness of cell 88. As can beseen in FIG. 6, a reinforcing layer 104 is included on one side ofairbag 76 at circle 98. Reinforcing layer 104 is another layer of fabricsized just larger than circle 98 in this embodiment, and is stitchedtogether with the fabric forming airbag 76. Each of ovals 56 alsoinclude a reinforcing layer 106 sized just larger than the oval. In some30 liter airbag embodiments, a reinforcing layer that is ½ inch largerat each edge than the stitching has been used. In still furtherembodiments, a reinforcing layer has been used on either side of theairbag, yielding a structure with four layers in the area beingreinforced.

Referring now to FIG. 6, the construction of reinforcing layer 104 maybe described in more detail. First layer 108 and second layer 110 formrespective sides of airbag 76. Sewn circle 98 is formed by stitching112, which extends through first layer 108, second layer 110, andreinforcing layer 104. The advantages of using reinforcing layer 104will be discussed later. Note, however, that other configurations,including the use of multiple reinforcing layers on either or both sidesof the airbag, are contemplated by the present invention.

The novel airbag disclosed herein is designed so the flow of gas betweenchamber cells is substantially reduced during the loading of the airbag.By creating a more reduced gas flow between the chamber cells duringloading, the pressure within a given substantially isolated cell buildsup greater than would otherwise occur with an open flow between the samecells. The increased pressure within the cell due to flow restriction orcross-cell flow restriction resists the occupant from striking throughthe cell to a greater extent than with conventional open flow betweencells. With the gas restricted in its movement out of the cell, anincreased resistance to occupant displacement or strike through isestablished. Therefore, the present invention provides airbags andmethods of making airbags that restrict flow between chamber cells.

What is meant by “striking through” or “penetrating through” the airbagis that the occupant's energy directed toward the airbag is not entirelydissipated prior to the occupant hitting a structure of the vehicle, anintruding object such as a pole, another vehicle, or the ground during arollover event. That is, during strike through, the resistive forceapplied by the pressurized airbag to the occupant is insufficient tostop the movement of the occupant prior to making contact with a solidstructure.

Because of the restricted flow between adjacent cells, the pressuredelivery from the inflator to the cells may require a more precisedesign of the gas delivery system to provide each substantially isolatedcell with its required operating pressure. For example, one suchdelivery method to achieve gas delivery to the individual cells mayutilize an elongated tube (for example, delivery tube 46) extendingwithin the upper portion of a side curtain airbag. The tube may befabricated with the appropriate size, quantity, and location of outletorifices to sufficiently deliver the appropriate amount of gas to eachcell. Additionally, scoops configured to channel flow into a given cellmay be utilized to further control the desired gas delivery. The scoopsmay be advantageous in areas of the delivery tube where the gas flowingin the tube tends to substantially pass by outlet orifices in thedelivery tube due to the dynamics of the supersonic gas flow within thetube. When the tube has a scoop, which is essentially an indentedsection of the tube including an opening, the gas flowing within thetube is channeled into a particular cell.

The scoops may be staggered or staged along the delivery tube to achievethe required channeling of gas into each cell. For example, one cell mayhave two or more scoops but would preferably not have them directly“in-line” with each other along the longitudinal axis of the deliverytube. Instead, the scoops are preferably staggered to better or moreeffectively capture and channel the gas flowing within the tube into thecell.

The restrictive flow of the present invention may be characterized usingthe term “diode.” The term “diode” is generally used in electronics torefer to a device that freely passes electrical current in one directionbut not in the opposite direction. In the present invention, “diode” isused to refer generally to the restriction of flow between airbag cells.This “diode effect” is due in part to differences in pressures; duringinitial filling of the cells the gas pressure within the delivery tubeis very high, yet the gas pressure within each pressurized cell iscomparatively much lower after inflation. Thus, the gas flow into eachcell occurs quite quickly, while the gas flow out of the cells and intoadjacent cells, into the delivery tube, or to the atmosphere iscomparatively slow.

One way to keep the gas from escaping the cell is to appropriatelydesign how the airbag fits around the delivery tube between cells. Thefollowing example is characteristic of the fit between the delivery tubeand the airbag between cells. The delivery tube is inserted between thetop perimeter seam and the ovals. The ovals assist in isolating thecells or regions from each other. Given a ⅝ inch delivery tube outerdiameter, the distance between the top perimeter seam and the oval'sseam may be in the range of 1.02 inches to 1.10 inches (with the fabricsewn flat-no pressure). The ⅝ inch delivery tube outer diameter wouldhave a circumference of 1.96 inches nominal. A distance of 1.02 to 1.10inches between the oval's seam and the top perimeter seam yields aninner circumference of about 2.04 inches to 2.20 inches when expanded bythe tube insertion. The clearance between the tube and the fabricopening provides enough clearance to allow for installation. However,the fit between the delivery tube and the airbag still provides enoughflow restriction between the tube outer diameter and the airbag fabricto restrict the gas flow between chambers (i.e. cells).

The difference in effective flow area between cells in a conventionalopen flow airbag and that of an airbag in accordance with the presentinvention is shown in the following example. A probable effective flowarea from the delivery tube into a diode cell to meet initial sideimpact fill requirements may have an effective flow area in the range of0.05 square inches to 0.15 square inches for a 30 liter side airbag.This effective flow area from the tube orifices is in addition to theeffective flow area occurring from the clearance between the deliverytube outer diameter and the fabric layers sewn around the delivery tubein areas between the cells. Various clearances between the delivery tubeouter diameter and sewn fabric layers surrounding the tube between cellsmay be used, yielding different effective flow areas. For example, witha 2.04 inch fabric circumference around the tube, the maximum possibleflow area between a ⅝ inch tube outer diameter and the fabriccircumference would be about 0.025 square inches. With the same tube anda 2.2 inch fabric circumference, the maximum flow area would be 0.078square inches. Given the larger 2.2 inch fabric circumference and thelarger of 0.15 square inch flow area from the tube orifices, the maximumeffective flow area between adjacent diode cell might be 0.23 squareinches.

In a conventional airbag, the flow area, even if restricted by a 1 inchdiameter opening between cells is around 0.8 square inches. A 1 inchdiameter opening between cells is actually toward the much morerestrictive end of current conventional airbags; many, if not all, haveeven larger open flow effective flow areas. The effective flow areadifference in this example would yield 3 to 4 times more open flow areain the conventional design as compared to the diode design discussedabove. The range of effective flow areas given for the diode design ofthe present invention is only an example for illustrational purposes andis not intended to limit designs into that range. Depending on cellsizes, cell volumes, or even timing requirements for filling the cells,the effective flow area requirements may change. Thus, for differentsized airbags, different effective flow areas may prove effective.

The diode airbag was tested with varying fits or clearances between thetube outer diameter and the fabric between the cells. When the effectiveflow area between the tube outer diameter and the fabric between thecells went beyond 0.3 square inches, the chances for strike-throughincreased. The flow area became too great between cells, thus not aseffectively increasing the pressure within the cell during loading ofthe cell by the mass. Therefore, it was determined that anything underan effective flow area of 0.5 square inches (flow area between fabricand tube plus the flow area from the orifices) between the adjacentcells may provide effective protection in some 30 liter airbagapplications. Under 0.25 square inches flow area proved to be even moreideal.

It should be noted that cells not on the ends of the air bag may havealmost double the maximum flow area of end cells, since flow can escapefrom a loaded interior cell into adjacent cells on both the left and theright. Because of this, the cells at the end of the airbag (the cellswith only one adjacent cell) may become stiffer than interior cells (thecells with two adjacent cells) during occupant loading. The extrastiffness of the end cells should be taken into account in designing theairbag.

The gas pressures within the inflated cells of the present invention aresubstantially low in comparison to the pressures within the deliverytube during inflation of the cells from the inflator. Typically, a sideairbag inflates during approximately the first 25 milliseconds afterbeing triggered. The occupant interaction with the airbag may initiatearound 30 milliseconds in some applications or as late as approximately55 milliseconds or more in others. Thus, by the time the occupant isloading or interacting with the airbag cell the pressure within thedelivery tube has dropped substantially. By this time, the pressure inthe delivery tube may actually come close to or equalize to thepressures within the airbag cells. For example, the pressure within thecells may be between 20 to 40 kpa while the pressure within the deliverytube may be 500 kpa to 1500 kpa during initial cell filling from theinflator.

As the occupant loads the cell and increases the cell's pressure, thegas within the cell may use the delivery tube outlet orifices as a cell“vent”. By the gas flowing back through the delivery tube holes andessentially being vented back to other cells in the airbag, the cell iskept from becoming excessively hard. The general goal is to havedelivery tube outlet orifices sized with a large enough total effectiveflow area to achieve the required fill timing for a given cell whilebeing small enough to restrict the backflow, along with the flowrestrictions from the fit between the delivery tube and airbag and seamoptimization, to achieve desired cell pressure increases during occupantloading.

Due to the advantages of the present invention, lower cell operatingpressures may be utilized with the present invention compared to thepressures needed in similar cell inflated cross-sections using aconventional open flow construction between airbag cells. The operatingpressure is the pressure the inflator must deliver to the airbag priorto occupant interaction (cell loading) to effectively dissipate theoccupant's energy prior to striking through the airbag. The loweroperating pressure requirement offered by the diode design isadvantageous over previous art since a reduced inflator output can nowachieve similar overall occupant protection performance. For example, anairbag without the more restrictive flow design of the present inventionwould require a higher output inflator (larger size) to fill the cellsto a higher required operating pressure. A reduced output inflator orsmaller size inflator required with the present invention may offer theadvantages of lower cost, lower weight, and less space required topackage the inflator within the vehicle.

Another possible advantage of a diode airbag is the ability to reducethe overall volume of each cell while retaining desired occupantprotection properties. Reducing the cell inflated thickness of aconventional airbag will achieve this lowering of the volume, but willrequire an increased cell operating pressure over that of a thickerinflated cell to achieve similar occupant protection. Because of thesmaller cell volume that may be required with the present invention,faster fill times and faster in-position times may be possible. This canbe achieved since it typically takes less time to fill a smaller cellvolume.

In the case of a diode design using a thicker cell cross-section (say4-5 inches), the pressure could be approximately 20 kpa to meet currentimpact requirements. Reducing the cell volume long with the cellinflated thickness to about 2.5 to 3 inches would require an increasedoperating pressure of around 60 kpa. The same size inflator, however,could be used for each approach. The advantage of the 20 kpa approach isthat it may apply less stress to the seams and thus, reduce overalllower airbag leakage. The approach with the 60 kpa and lower cellthickness/volume could give the advantage of faster in-position timesfor the same inflator output. Depending on the specific applicationrequirements and goals, either approach may be implemented.

Alternatively, a soft or flexible delivery tube may be utilized insteadof a rigid or solid tube. Even a delivery tube constructed from fabricwith appropriately staged outlet holes may be utilized for appropriategas distribution to the individual cells. While more versatility andtunabilty may be allowed by using a rigid delivery tube (due to theability to shape the tubing wall contour with scoops), the use of a morecollapsible (flat lying) tube may have packaging benefits for someapplications.

With a solid delivery tube, the scoops which are utilized to channel gasflow into a particular cell region can more efficiently achieve a highflow rate of gas into the cell without disrupting the more efficientlaminar flow within the delivery tube. In some solid delivery tubes usedfor gas delivery into conventional airbags, the outlet orifices arecreated by perforating the tubing wall. In these cases, the perforatedtube wall creates an obstruction within the tubing internal diameter. Inaddition to restricting the effective flow area to the remainder of thetube, the perforations create a more turbulent gas flow within the tube.Turbulent flow compared to a more laminar flow is known to createincreased pressure losses. The more turbulent the flow within a deliverytube, the more these pressure losses may add up, which may lead toinefficient use of the gas energy delivered from the inflator. Thus,more effectively optimizing the delivery tube with appropriatelypositioned scoops for each individual cell, will use the inflator's gasenergy more efficiently.

While a diode-type airbag could be used with any of a number ofinflators known in the art, an extended output inflator may work betterthan some other inflators in roll-over applications. An example of anextended output inflator is shown and discussed in U.S. Pat. No.6,543,806 to Fink, the entire disclosure of which is herein incorporatedfully by reference. One of the aspects giving the extended outputinflator a performance advantage is the use of a gas mixture containedtherein. One gas with a small molecular size, such as helium, incombination with a gas with a larger molecular size, such as argon,nitrogen, carbon dioxide, nitrous oxide, etc., may be utilized.

A smaller molecule gas, such as helium, may be utilized because it hasbeen shown to more rapidly fill an airbag. This likely is because heliumhas a lower molecular weight of 4. For example, argon is a highermolecular weight gas with a molecular weight of almost 40. The heliummolecules flow more quickly through a given flow area than a larger gasmolecule, such as argon.

The initial inflation of the airbag cells from the stowed state to theinflated state typically needs to occur within 15 to 25 milliseconds(in-position time) after a signal is received from a crash sensor.In-position time is the time required for the airbag to deploy from thestowed state within the roofline of a vehicle to a substantiallyunfolded and inflated position covering the vehicle's interior sidestructure. Thus, helium in a gas mixture may give the pressurized gasmix the ability to quickly flow into the airbag to meet the requiredin-position timing. Helium however, due to its small molecular size,will have a greater tendency to leak through any potential leak paths inthe airbag than would a higher molecular size gas. Therefore, a highermolecular size gas within the pressurized gas mixture, such as argon,gives this pressurized gas mix the characteristic of a slower leak ratethrough any airbag leak paths. A gas mixture can therefore be optimizedto meet both demands, fast in-position time and low leakage, byutilizing the best mixture percentage scenario to meet particularapplication requirements.

It has been found that a cold gas inflator containing only a highermolecular size gas, such as argon, may not achieve the required 15-20millisecond in-position fill timing alone. In a cold gas inflator, thegas within the bottle undergoes decompression during inflation and coolsrapidly. The larger size gas molecules become more sluggish compared toa smaller size molecule when cooled. This sluggishness has to do witheach gas's critical temperature. The larger the gas molecule, the higherthe gas's critical temperature. The closer a gas comes to its criticaltemperature during cooling from decompression, the slower the randommovement of the molecules becomes. Thus, a higher molecular weight gaswill become more sluggish as it is cooled than will a lower molecularweight gas. Therefore, in general, the flow rate of a higher molecularweight gas will be lower through a given outlet area as compared to asmaller molecular weight gas.

Finding an optimum mixture of high and low molecular weight gases isimportant to the functionality of an airbag. The ideal gas mixture willdepend on the application or, more specifically, on the internal volumeof the airbag and the fill timing requirements. It has been found thatairbags of a smaller internal volume, for example around 25-35 liters,may allow for a higher concentration of argon in a helium-argon mixturewhile meeting required fill times or in-position timing. As discussedabove, providing the airbag with as high a concentration of the largergas molecule as appropriate will achieve better gas pressure retentionover time in the airbag. In particular, higher pressure retention overtime is desired when rollover protection is a concern.

In larger airbag volumes, the concentration of argon may need to bereduced to assist in meeting required in-position timing for the largervolume being filled. Typical gas mixtures for smaller airbags may rangefrom 60% helium/40% argon to 75% helium/25% argon. For the larger airbagvolumes (40 L and up), the ratio of helium may need to be increased.Typical ratios found effective may range from 65% helium/35% argon to80% helium/20% argon. These ratios are typical of ranges found effectivewith conventional open flow airbags.

As disclosed herein, the diode airbag designs allow for higherconcentrations of argon due to techniques achieving faster in-positiontimes more independent of the gas mix ratio. Again, these possiblehigher concentrations of the larger gas molecule will further enhanceairbag pressure retention. Mixtures have been used with a cold gasextended output inflator or even in a single chambered cold gas inflatorin the range of 50% helium/50% argon. This particular mixture providedin-position times in the 40 millisecond range. Thus, depending on filltiming requirements (longer in-position time requirements allowincreased argon ratios), the concentration of the larger gas molecule,such as argon, may range from 10% to 100%.

Effusion is the rate at which a gas will pass through a porousbarrier/hole/orifice or any mall potential leak path or opening.Effusion, as it applies to airbags, relates to the tendency of smallergas molecule, such as helium, to leak through the airbag leak paths tothe atmosphere at higher rate than a larger gas molecule, such as argon.

Once in the airbag, the larger gas molecule within the gas mixture mayeffectively act as a “blocker” to restrict the leakage of some of thehelium molecules through the seam openings or other leak paths. If thelarger argon molecule were not also randomly escaping through the leakpaths, the helium molecules would escape more unrestricted or morefreely through the leak paths. The helium molecules may now collide withthe larger argon molecules, thus diverting a path which would haveotherwise met directly with the atmosphere. In effect, the overall gasleakage is reduced.

Another airbag characteristic that has an influence on the requiredinflator gas mix ratio is the airbag's operating pressure. A distinctadvantage of the lower operating pressure diode airbag of the presentinvention is that the gas mixture ratio may allow for a higherconcentration of the larger gas molecule, such as argon. A diode airbagmay be inflated to operating pressures of about 20-40 kpa as opposed toconventional open flow designs requiring around 60-120 kpa. Because adiode airbag has a lower operating pressure, a smaller amount of gas ina smaller inflator is necessary.

Additionally, a lower airbag operating pressure allows for reduced seamleakage and reduced stress to the seams. Also, it is easier for anextended output inflator to effectively maintain a lower operatingpressure over an extended period of time than it would be for theinflator to maintain a higher required operating pressure. Therefore,the combination of an extended output inflator and a diode airbag designcan offer significant system level advantages.

Another advantage of a lower operating pressure airbag may be reducedinjury to out-of-position occupants. In some situations, an occupant maybe in a position very close to a deploying airbag. Airbags are requiredto deploy at extremely fast rates and have been known to cause injury tooccupants who intrude on the deployment path of an inflating airbag. Oneaspect having an influence on potential injury to the out of positionoccupant is the internal airbag pressure. The diode airbag of thepresent invention would effectively reduce the force experienced by theout-of-position occupant because of its lower internal pressure over agiven surface area.

Additionally, as an airbag “tuning” benefit, the diode airbag may bedesigned to deliver a relatively higher pressure to only some of thecells within an airbag. It is possible to achieve a higher pressure in aselected cell(s) over the initial filling/occupant interaction event,approximately the first 20-60 milliseconds. If, for instance, certaincells would perform better with higher pressure over the initialoccupant impact, tuning these cells may be advantageous. For example,cells known to interacted with an occupant during a vehicle or poleimpact may be tuned to a higher pressure. Once the selected cellsreceive the higher pressure to meet the requirements for the initialside impact, the pressures within that particular cell may equalize withthe remaining cells as the gas is gradually transferred back through thedelivery tube outlet orifices.

A further performance “tuning” advantage with the diode approach is tohave particular cells receive gas at a faster rate than other cells.Delivering gas at a faster rate to selected cells may yield fasterin-position timing. This will allow the selected cells to pull theremainder of the airbag down and be in the fully deployed in-positionstate faster than if all the cells received equal amounts of the initialgas delivery. The cells targeted to be the cells to receive the higherpressure can also be the same selected to cells to have the fasterfilling times. These two objectives of higher cell pressure and a fastergas delivery rate work well together.

Another option with the diode approach is to create particular cell(s)or cell regions that inflate over a longer period of time. These cellscould be cells that are not required during the initial side impact, butare needed in time for a rollover type event. This may be achieved byhaving delivery tube outlet orifices with an effective flow areasubstantially smaller than that of the tube orifices used for fillingthe cells needed for the initial side impact. These smaller outletorifices could be in direct communication with the slower filling cells.Instead of these slower filling cells filling in the 15-25 millisecondtime frame, they could fill relatively slower, 100-500 milliseconds oreven longer, for example.

By using the slower filling cell option, less inflator output may berequired for the initial side impact requirement because less totalvolume is required to be filled. Then, the cells that fill over thelonger period of time need to fill only to a lower pressure compared tothe initially faster filled cells, as much as half the pressure or less.Thus, the total inflator output requirement is reduced by staging theinflation of selected cells. Yet, the total protection area is providedas needed, when and where it is needed.

In particular, slower filling cells could be cells which fill to provideprotection on the roof area or ceiling of the vehicle. These cells wouldnot necessarily be required during an initial side impact event, butwould provide benefit during a rollover event. The time requirement forthese cells to fill may be relatively much later in time to that of thecells utilized during the side impact event.

With the inflatable cells filling for roof protection, there may not beas much room between an occupant's head and the roof. Especially withlarger or taller occupant's, this will be the case. For the cellsintended to cover a larger surface area within the roof liner, theairbag can alternatively be stowed in an unfolded condition within theroof liner. This would allow for essentially immediate or pre-existingin-position timing and reduce concerns about airbag positioning in caseswith taller occupants.

Another application for slower filling cells could be to expand theinflated airbag cell coverage area over the side structure of thevehicle. This provides expanded protection in a vehicle rollover, as theoccupant may be tossed around and come into contact with areas of thevehicle not typical of non-rollover events.

It is possible that areas within a particular airbag which were notintentionally designed to fill with gas may fill gradually over time.The reason for these additional unintended cells may be the fact thatseams used to close-off these un-inflated airbag areas actually allowleakage through the seams and into the unintended cell area. As anextended output inflator continues to supply pressure to an airbag,these unintended cells fill with gas. Depending on the degree of leakagein the seam, the time it takes for the unintended cells to fill mayvary. In one particular airbag, the unintended cell filled inapproximately 1 second, as viewed on video monitoring of the deployment.Optionally, the offending seams creating the unintended cells may bestrategically opened, creating slower filling cells. Furthermore, thetotal tension in the airbag may be further increased by the expansion ofthese slower filling cells over time.

Occupant containment is another demand required of an airbag. Occupantcontainment is the ability of a deployed airbag to keep the occupantwithin the vehicle, preventing possible ejection of the occupant througha window opening. Airbag tension over a window opening has an effect onthe degree of containment or occupant displacement beyond the windowopening. With an airbag in accordance with the present invention, it islikely that less displacement of the cell at the airbag cross-sectionlevel will occur. This may translate into less total occupant excursionwhen compared to a similar cell inflated cross-section at the samepressure level using conventional open flow between cells, which likelywould deform to a greater extent.

Yet another option that could be added to an airbag in accordance withthe present invention is inflatable straps. Straps are often used toanchor an airbag to the vehicle. Having the straps inflate will decreasetheir length as compared to their un-inflated state, thereby creatingtension within the straps and the airbag to which they are affixed.Configuring the straps to inflate after the initial inflation of theairbag could advantageously add tension to the airbag at a time when itwould otherwise be losing tension due to pressure loss.

The following example highlights some of the advantages of the diodedesign of the present invention by comparison to a conventionallydesigned airbag. In this particular comparison example, a two-rowcoverage (A to C pillar) airbag with an approximate volume of 30 litersis used. The airbags in this comparison example were both cut and sewnairbag constructions without seam sealing and used a similar fabric.

The conventional open flow airbag has been found through dynamic poletesting to require an operating pressure of around 60-70 kpa to preventoccupant head strike through. The internal volumes of the airbags wereessentially held constant at 30 liters. The airbags were each subjectedto energy absorbing tests where a fixed mass is dropped from apredetermined height into each airbag in the same location/area. Also,similar inflated cross-section thicknesses were utilized. The mass usedwas a 6.5 inch diameter shape, which approximately simulates the surfacearea of an occupant head. Tests of both types of airbags revealed thatthe conventional open flow airbag required approximately two to threetimes more pressure to prevent the same mass energy from strikingthrough an airbag as compared to the pressure required by a diode airbagin accordance with the present invention.

This difference in the operating pressure requirement allows a diodeairbag to use a substantially smaller inflator. In the example above,simulating side impact protection only (non rollover), the inflatorrequirement in the conventional open flow airbag to yield 60 kparequires a 2.3 molar output cold gas inflator (He/Ar). The inflatorrequired by the diode airbag to meet an approximate 22 kpa operatingpressure is a 1.5 molar output cold gas inflator (He/Ar). Thus, theconventional airbag requires an approximate 50% higher molar outputinflator than the diode airbag. This is due in part to the loweroperating pressure requirement of the diode airbag, but also to thereduced airbag stress allowed by the lower operating pressures (lowerairbag leakage).

Using the same sewn/unsealed airbag examples, airbag/inflatorcombinations were then evaluated as they relate to rollover protection.It was determined that the conventional open flow airbag would requireapproximately 15 kpa at 5 seconds to sufficiently meet containmentrequirements, given a 5 second containment objective. Given that fixed 5second objective, a diode airbag will perform similarly on containmentobjectives with an airbag pressure of around 10 kpa at 5 seconds. Thispressure value for a diode airbag is estimated from the reduction indisplacement within the loaded cell cross-section on a diode airbagcompared to the conventional airbag. Through testing, it was determinedthat the conventional airbag required a 3.5 molar output cold gasExtended Output Inflator (EOI) to meet the approx. 15 kpa at 5 seconds.Preliminary testing also found that the lower operating pressure diodeairbag to requires a 2.5 molar output cold gas EOI to meet the 10 kpa at5 seconds criteria.

Seam sewing to reduce leak paths for enhanced pressure retention inunsealed airbags can also affect the performance of an airbag. Airbagleakage can be broken down into several key leak paths. First, leakagemay occur through the base fabric, which is more commonly referred to asfabric permeability. The permeability is the rate of gas leakage throughthe fabric structure or through the thread weaves. Several methods canbe employed to reduce or effectively eliminate this potential leak path.One conventional method is to coat the fabric with a gas impermeablesubstrate such as silicon. Other coatings such as neoprene,polyurethane, polyester, etc. or others may be used. Another commonlyknown method is the use of laminates. Yet another method to reducefabric permeability is dipping a fabric in a solution that penetratesand bonds/adheres to the fabric creating a barrier to leakage.

In the fabrics coated with silicon, it has been found that higher levelsof coating help to reduce airbag leakage. A typical coating level usedin a popular 420 denier nylon fabric is 0.7 ounce per square yard ofcoating. At this coating level, the permeability may be substantiallyreduced compared to a non-coated fabric. However, some permeability ispresent, especially as the pressures are increased.

In side curtain applications, the airbag operating pressures are wellabove atmospheric pressure. A typical pressure could be 50 kpa to 120kpa and beyond. At these higher pressures and with the large surfaceareas required to make up a side curtain, the impact of the fabricpermeability more substantially affects the total airbag leak rate. Thisis especially true as the time requirements for maintaining an inflatedairbag increase. The fabric permeability may be low compared to uncoatedfabrics but even small amounts can surely add up when considered intotality over the entire surface area of the airbag.

A second leak path exists in areas where a seam is used to join fabricpanels. One commonly practiced method to create a seam is to sew thefabric panels together using stitching (sewn seams). With a sewn seam,several potential leak paths exist. One leak path exists between thefabric panels as the panels are sandwiched together by the sewn seam.That is, leakage may occur between the fabric layers through theperimeter opening of the fabric. Increasing the density of the stitchingmay also reduce leakage.

Yet another leak path exists where a needle hole is created during thestitching process as the needle thread is passed through each panelfabric layer. As the stitching thread passes through the created needleholes, it will assist in blocking some gas flow. However, some degree ofleakage will still exist.

Another method used to reduce airbag leakage has been termed “Seal andSew”. This method utilizes an adhesive or sealant that is applied tofabric panels in all the areas that are needed to create the pattern andshape of the inflated airbag. Then, for increased strength andintegrity, a sewn stitch is added in the center of the sealant bead.While this method has been found to reduce airbag leakage and be apotential option for increased pressure retention, drawbacks exist. Theadhesive/sealants required are quite expensive. The application processhas been deemed “messy” and time consuming. The needle passing throughthe adhesive bead can pick up contaminants from the sealant bead, whichmay then negatively affect the sewing process. A cure time is alsorequired after applying the adhesive bead prior to sewing. Anothersubstantial drawback with the “seal and sew” method is that the seamrequires an increased package size when the airbag is folded and storedin the stowed position in the vehicle roof line area.

A fabric type known for low permeability is disclosed in Published U.S.Patent Application 2004/0242098 A1 (the '098 application) to Bass,published on Dec. 2, 2004 and incorporated herein by reference. Such afabric has advantages for reduced leakage due to its extremely lowpermeability, while also displaying favorable leak preventioncharacteristics at the seam level. The treated fabric has been found tohave reduced leakage at the needle hole leak path as compared to otherfabric alternatives. Such a fabric also appears to more effectively moldaround the thread and create a better seal against gas escaping throughthe needle hole.

Another common seam construction method is called OPW or One PieceWoven. This process weaves the fabric panels together to create aninterconnected seam as the fabric is passed through a loom. This methodyields fewer leaks because no thread is used. However, OPW is stillsusceptible to seam stress from inflation, and leak paths may be createdin these seam areas.

Because a smaller needle size generally yields less leakage, severalcombinations of thread sizes and needle types/sizes were explored. Threedifferent thread sizes were used (#138, #92 and #69 thread sizes). Themost commonly used thread size in automotive airbags is the #138 size innylon. After matching each thread size with the best needle toefficiently deliver the thread without breakage or seam inconsistencies,the thread size/needle combinations were tested to comparativelyevaluate seam leak rates.

To more effectively evaluate seam leakage and compare multitudes ofvariables (such as seam density, thread size, needle size, needle pointtype, thread type, thread brand, bobbin thread tension, needle threadtension, and fabric type), fabric swatches were sewn together to createmultitudes of small inflatable square shaped “pillows.” The testspecimen pillows were used to evaluate seam leakage at the outer pillowperimeter seam along with a circular seam sewn in the center. Fourfabrics were used for comparisons with the varying seamconstructions—fabric disclosed in the '098 application in 315 and 420denier and silicon coated 315 and 420 denier fabric (both havingapproximately 1 oz/sq yd of coating).

The test pillows were pressurized to pressures of both 20 kpa and then60 kpa and maintained at each of those levels during leak evaluations.Three methods were used to evaluate the leakage—submersion of thepillows with visual observation, spray of the seam with a bubble leakcheck solution and lastly, electronically monitoring the pressure decayafter shutting off the supply pressure.

The seam in the center was chosen to simulate a higher stressed typeseam that is typical of many side curtain airbag patterns. These typesof higher stressed seams are those that have the airbag inflatable areaspulling up on the seam around substantially the entire seam perimeter.In addition, these seams are typically of relatively small size so as tonot add too large of an un-inflated area within a required protectionzone of the airbag. Therefore, these higher stressed seams have arelatively small seam length (circumference) exposed to some of thehighest forces occurring within the inflated airbag. These higherstressed seams generally occur in the inner areas of the inflated sidecurtain. It is these higher stressed seam areas which generally developthe most notable degree of leakage under pressurization. Thus, findingthe best solutions to reduce leakage on these highly stressed seams willprove quite beneficial for enhanced airbag pressure retention.

Through testing, it was discovered that by adding an additional smallfabric layer to the exterior side(s) of the airbag, substantiallyreduced leakage resulted. This is advantageous in areas that undergomuch higher stresses during inflation and pressurization. Thereinforcements could be small circular cutouts covering the circularcenter seam.

Externally positioned reinforcements serve a dual purpose. First, theyadd additional fabric strength to the highly stressed seam area, thuseffectively reducing the spreading apart of the fabric weave. Second,the fabric layer takes on a gasketing effect to reduce the leakage whichwould otherwise flow more easily through the needle holes.

Comparative tests were also conducted with the reinforcing layer(s)positioned on the inside of the pillow surfaces or within the pressureboundary. Positioning on the inside showed substantially less promise inreducing leakage. Some minor benefit was realized by adding strength orresistance to the spreading of the outer fabric weave, but the overallleakage in these stress point areas were still substantially higher thanwith the fabric reinforcing layer sewn on the outside surface orexterior sides of the pillow.

Therefore, in higher stressed areas of an airbag, externally positionedreinforcing layers can improve pressure retention. Both the siliconcoated fabric reinforcing layers and the '098 application fabricreinforcing layers were found effective when positioned externally. The'098 application fabric showed an edge over the silicon coated fabric.The silicon fabric displayed better results with the coated surfacefacing the airbag.

The results related to seam density along the perimeter showed that inall the fabric types a higher seam density provided lower overallleakage. A seam density of 18 to 22 stitches per inch with a #92 threadbeing preferable. As the density was increased beyond approximately 24stitches per inch, no appreciable reduction in leakage was seen with anyof the thread sizes. A #92 thread allows for approximately 50% morethread length to be wound onto the bobbin case/spool compared to a #138thread. This allows for reduced change-over times when replacing thebobbin spools. Also, the smaller #92 thread cross-section reduces theseam thickness, which has advantages when the airbag is folded.

It was also discovered that too low a bobbin tension resulted increasedleakage. The lower bobbin tension is not as effective in bunchingtogether the fabric to better restrict leakage in the seam. So, acombination of an appropriate higher bobbin tension combined with aneedle tension of approximately 2-4 times more than the bobbin tensionhave been found quite effective in reducing leakage. Also, a polyesterthread with silicon additive has been found to process through themachine/needle more effectively than even a same thread size #92 innylon.

Utilizing a cold gas inflator for the inflation of the airbag allows forthe use of a polyester thread. Conventionally, many airbags utilizedinflators with hotter gas outputs, and, therefore, required nylonthread, or in some cases even threads with higher temperature resistancesuch as brands of Kevlar or Nomex. In the case of using a cold gasinflator, the use of a polyester thread type is possible.

A combination found most effective is the use of a polyester Coatsbrand, #92 thread size of bonded construction, with a silicon additive.The needle found most effective is a 100-16. The needle point type foundmost effective is an RG. This type of needle will produce less cuttingor abrasion of the fabric during sewing, while not adversely affectingthe leak rate. The tension for the bobbin thread found most effective is6-9 ounces. A corresponding effective tension for the needle thread wasfound to be 18-25 ounces.

Additionally, the elongation of the different thread types were found tohave an effect on leakage. Generally, a stiffer thread yields a lowerleakage rate during airbag pressurization. Too stiff a thread mayadversely affect the stitch breaking strength, but a thread such as abonded polyester has been found quite effective. A thread utilizing ahigher content of silicon coating or treatment could prove to be evenfurther advantageous for reducing sewn seam leakage.

Several techniques in sewing the actual patterns into the airbag havealso uncovered advantages for reduced leakage. Some of these methods canalso improve upon process time while providing favorable seam uniformityand consistency. In sewing the smaller circular, oval, oblong, etc.shaped patterns, utilizing a programmed machine can provide superiorseam uniformity. These program machines move the fabric in the circularpattern without the need for turning the entire airbag through a 360rotation.

It has also been noted that the utilization of a single seam to connecta centrally located seam (circular for example) back to the airbagperimeter seam also may reduce leakage. The number of needle holescreated for this connecting seam is reduced by about half when comparedto a conventional dual seam.

Another feature found helpful for reducing leakage is to fold the airbagat the bottom perimeter as opposed to using a seam and two separatefabric panels. This technique is known in the industry as a “taco fold.”

While one or more preferred embodiments of the invention have beendescribed above, it should be understood that any and all equivalentrealizations of the present invention are included within the scope andspirit thereof. The embodiments depicted are presented by way of exampleand are not intended as limitations upon the present invention. Thus,those of ordinary skill in this art should understand that the presentinvention is not limited to these embodiments since modifications can bemade. Therefore, it is contemplated that any and all such embodimentsare included in the present invention as may fall within the scope andspirit thereof.

1. An inflatable airbag assembly for a passenger vehicle, said airbagassembly comprising: an airbag having a plurality of substantiallyisolated cells; a delivery tube having a plurality of outlet orificesfor supplying an inflation gas to the plurality of substantiallyisolated cells; an upper restraint for the delivery tube; a series ofdiscrete stitchings located between the substantially isolated cells,the series of discrete stitchings each forming a lower restraint for thedelivery tube; and wherein, upon inflation of the plurality ofsubstantially isolated cells with the inflation gas, flow of gas betweeneach of the plurality of substantially isolated cells is restricted bythe series of discrete stitchings and the upper restraint.
 2. The airbagassembly of claim 1 wherein at least one of the plurality of outletorifices includes a scoop configured to direct the inflation gas throughthe at least one of the plurality of orifices.
 3. The airbag assembly ofclaim 1, wherein each of the plurality of outlet orifices includes ascoop configured to direct the inflation gas through the plurality ofoutlet orifices.
 4. The airbag assembly of claim 1, wherein theplurality of outlet orifices are staggered about the delivery tube andeach of the plurality of outlet orifices has a scoop for directing theinflation gas through the plurality of outlet orifices.
 5. The airbagassembly of claim 1, wherein the series of discrete stitchings and theupper restraint define an effective flow area between an exterior of thedelivery tube and the upper restraint and each of the series of discretestitchings, wherein at least one effective flow area is greater than 0and less than 0.5 square inches.
 6. The airbag of claim 5 wherein theeffective flow area is greater than 0 and less than 0.25 square inches.7. The airbag assembly of claim 1 wherein the inflation gas is providedby an inflator for a time period in the range of 100 to 500milliseconds.
 8. The airbag assembly of claim 7 wherein an operatingpressure of the plurality of substantially isolated cells is about 20 to40 kilopascals, the operating pressure being provided by the inflationgas.
 9. The airbag assembly of claim 7 wherein the percent by weight ofa large molecule gas within the inflator is between 10% and 40% and theairbag is filled by the inflator to a substantially full volume in about15-20 milliseconds.
 10. The airbag assembly of claim 9 wherein the largemolecule gas is argon.
 11. The airbag assembly of claim 7 wherein thepercent by weight of a large molecule gas within the inflator is about50% and the airbag is filled by the inflator to a substantially fullvolume in about 40 milliseconds.
 12. The airbag assembly of claim 1wherein the delivery tube is rigid.
 13. The airbag assembly of claim 1wherein the delivery tube is flexible.
 14. The airbag assembly of claim13 wherein the flexible delivery tube is constructed of a fabric. 15.The inflatable airbag assembly as in claim 1, wherein the delivery tubeextends in a first direction and each of the series of discretestitchings have a curved portion extending at least partially in thefirst direction and an apex of the curved portion defines a portion ofan effective flow area between an outer surface of the delivery tube andthe upper restraint.
 16. The inflatable airbag assembly as in claim 1,wherein each of the series of discrete stitchings secure a separatepiece of reinforcing fabric to an exterior surface of the airbag.
 17. Aninflatable side curtain airbag assembly for protecting an occupant of apassenger vehicle, said airbag assembly comprising: an airbag having aplurality of substantially isolated cells formed by joining together afirst layer and a second layer; a delivery tube having a plurality ofoutlet orifices for supplying an inflation gas to the plurality ofsubstantially isolated cells; an upper restraint for the delivery tube;a series of discrete stitchings located between the substantiallyisolated cells, the series of discrete stitchings each forming a lowerrestraint for the delivery tube; wherein, upon inflation of theplurality of substantially isolated cells with the inflation gas, flowof gas between each of the plurality of substantially isolated cells isrestricted through an effective flow area defined by the upper restraintand the series of discrete stitchings between each adjacent cell of theplurality of substantially isolated cells and wherein at least oneeffective flow area is greater than 0 square inches and less than 0.5square inches; and wherein at least two of the plurality ofsubstantially isolated cells are located adjacent to one another. 18.The airbag assembly of claim 17 wherein the effective flow area betweeneach adjacent cell of the plurality of substantially isolated cells isgreater than 0 square inches and less than 0.25 square inches.
 19. Theairbag assembly of claim 17 wherein the first layer and the second layerare stitched together using thread to form a stitched seam.
 20. Theairbag assembly of claim 19 wherein the stitched seam is sealed.
 21. Theairbag assembly of claim 19 further comprising a reinforcing layer inhigh stress areas of the stitching.
 22. The airbag assembly of claim 17wherein the first layer and the second layer are joined using a onepiece woven construction.
 23. The airbag assembly of claim 17 whereinthe first layer and second layer are comprised of fabric.
 24. The airbagassembly of claim 23 wherein the fabric is a coated fabric.
 25. Theinflatable side curtain assembly as in claim 17, wherein the deliverytube extends in a first direction and each of the series of discretestitchings have a curved portion extending at least partially in thefirst direction and an apex of the curved portion defines a portion ofthe effective flow area.
 26. The inflatable airbag assembly as in claim17, wherein each of the series of discrete stitchings secure a separatepiece of reinforcing fabric to an exterior of the airbag.
 27. Aninflatable airbag assembly for a passenger vehicle, said airbagcomprising: an airbag having a plurality of substantially isolatedcells; a delivery tube having a plurality of outlet orifices forsupplying an inflation gas to the plurality of substantially isolatedcells; an upper restraint for the delivery tube; a series of discreteareas located between the substantially isolated cells, the series ofdiscrete areas each forming a lower restraint for the delivery tube; andwherein, upon inflation of the plurality of substantially isolated cellswith the inflation gas, flow of gas between each of the plurality ofsubstantially isolated cells is restricted by the series of discreteareas and the upper restraint.
 28. The airbag assembly of claim 27,wherein at least one of the plurality of substantially isolated cells isconfigured to inflate before another one of the plurality ofsubstantially isolated cells and each of the plurality of orifices islocated proximate to a scoop configured to direct the inflation gastherethrough and the configuration of the scoops determines which one ofthe plurality of substantially isolated cells is inflated first andwherein the configuration of the scoops directs the inflation gasthrough the plurality of orifices.
 29. The airbag assembly of claim 28,wherein the scoops are staggered about the delivery tube.
 30. Theinflatable airbag assembly as in claim 27, wherein the delivery tubeextends in a first direction and each of the series of discrete areasare a series of discrete stitchings each having a curved portionextending at least partially in the first direction and an apex of thecurved portion defines a portion of the effective flow area between andwherein each of the series of discrete stitchings secure a separatepiece of reinforcing fabric to an exterior surface of the airbag. 31.The occupant restraint system as in claim 27, wherein each of the seriesof discrete areas are formed by a one piece woven piece of fabric thatdefines the airbag.
 32. An occupant restraint system for use in apassenger vehicle, said system comprising: an extended output inflator;a sensor configured to send a signal to the extended output inflator ata desired time; a delivery tube having a plurality of outlet orifices,wherein the delivery tube is connected to the extended output inflator;an airbag having a plurality of substantially isolated cells an upperrestraint for the delivery tube; a series of discrete stitchings locatedbetween the substantially isolated cells, the series of discretestitchings each forming a lower restraint for the delivery tube; andwherein, upon inflation of the plurality of substantially isolated cellswith an inflation gas from the extended output inflator, flow of gasbetween each of the plurality of substantially isolated cells isrestricted through an effective flow area between each adjacent cell ofthe plurality of substantially isolated cells, wherein the effectiveflow area is between an outer surface of the delivery tube and the upperrestraint and the series of discrete stitchings and wherein at least oneeffective flow area is greater than 0 square inches and less than 0.5square inches.
 33. The occupant restraint system as in claim 32, whereinthe delivery tube extends in a first direction and each of the series ofdiscrete stitchings have a curved portion extending at least partiallyin the first direction and an apex of the curved portion defines aportion of an effective flow area between an outer surface of thedelivery tube and the upper restraint.